The HH6 has the option for Custom DNS so I hope that BT have moved away from it - for now I just use Google's IPv6 DNS instead, but again on all my machines only.
And where is this setting, my Smart Hub (i.e. HH6) doesn't have any section that allows you to change the Primary and Secondary DNS Addresses.
Unless I am missing a section.
BTBroadband - Infinity 4 - 310Mbps (down), 31Mbps (up)